In the computer industry, hard disk data storage elements or memory are generally made from aluminum or an aluminum alloy. Through any variety of processes, the aluminum is treated or otherwise coated and passivated so that it may act as a repository for information which is electronically written onto the disk. Coating and passivating a hard disk data storage element is generally undertaken to provide a surface which is both chemically and mechanically appropriate for use in a data storage environment. Mechanical coating and passivation of the disk covers defects and provides a surface which is capable of being polished and super finished. Chemical passivation of the disk includes the covering or sealing of any defect promoting constituents on the disk surface. One means of coating and passivating the aluminum is to apply a nickel phosphorous plating onto the aluminum disk drive.
Hard disk memory components have certain properties or characteristics which make them commercially practicable products. For example, hard disk components should be smooth or have an ability to be super finished to near atomic smoothness. The disk should also be free of defects such as holes, pits, digs, scratches and mounds. The disk should also be thin so that as many disks as possible can be packaged or placed in a disk drive. Fabricating a disk which is thin and has a low mass is also easier on the drive motor. The disk should also be hard and quite stiff. High stiffness, as measured by the modulous of elasticity, allows the disk to avoid harmonic vibration. One other attribute that the disks preferably have is a lower cost.
The conventional material used in this fabrication has traditionally been aluminum or an aluminum magnesium alloy. Coating this alloy with a nickel plate provides a hard exterior surface which allows the disk to be polished and super finished.
While the nickel plate on the exterior of the disk provides a certain level of hardness, the aluminum alloy used as the internal substrate of the disk is not ideal as it provides a relatively soft less rigid internal substrate. As a result, any shock to the file that is intense enough to lift the read/write transducer off the disk may create a defect in the nickel plate which will continue through to the aluminum substrate. In essence, the aluminum substrate of the disk provides no additional hardness or stiffness to assist in reducing the occurrence of defects.
One alternative to aluminum substrates for hard disks is the use of nonmetallic materials such as glass, glass ceramic, and ceramic. Various coating methods have been developed for coating these materials.
For example, Japanese patent 4280817 discloses a method for forming a thin zirconia film on a glass substrate. Zirconium n-propoxide, acetic acid and water are reacted to form a zirconia precipitate precursor gel, mixed with acetic acid and n-butanol, heated to 60.degree. C. coated and sintered onto the glass. The coated glass is thermally treated at 500.degree. C. to form cubic zirconia. Vong, U.S. Pat. No. 4,397,671, discloses a method for forming a metal oxide film on the surface of a heated glass substrate by forming a powder from an organic based metal salt which is heat decomposable, such as metal acetyl acetonates. There is no disclosure of forming a zirconia coating on the heated glass.
Additionally, Seebacher, U.S. Pat. No. 4,131,692, discloses a method for making a ceramic resistor by applying a solution of palladium chloride to the surface of a ceramic body and stoving in the coating, after which a second layer is formed by plating in a nickel bath.
Plumat et al, U.S. Pat. No. 3,850,665, disclose forming a metal oxide coating on a vitreous or nonvitreous substrate by applying to the substrate a composition comprising an acetyl acetonate coprecipitate of two or more metals. The substrate and composition are simultaneously or subsequently heated to convert the coprecipitate to a metal oxide coating. Among the metals which can be precipitated are mixtures of two or more of iron, nickel, cobalt, zinc, vanadium, copper, zirconium, chromium, manganese, yttrium, tungsten, and indium. Klinedinst, U.S. Pat. No. 5,118,529 discloses a method for coating titanium dioxide onto surfaces such as those comprising zinc sulfide, phosphor to provide for any number of enhanced properties including chemical resistance in absorbency, as well as the filtering or reflection of electromagnetic radiation.
Further, Schultze et al, U.S. Pat. No. 5,043,182 discloses a method for producing ceramic metal composite materials through the application of ceramics onto a substrate. Subsequently, molten metal is infiltrated into the pores of the ceramic material. Bradstreet et al, U.S. Pat. No. 2,763,569 discloses a coating method for use in the application of refractory metal oxide films onto metal parts which are subjected to high temperature during operations such as jet engines.
Even still, problems exist with the coating of nonmetallic substrates. Nonmetallic substrates such as, for example, glass, glass/ceramic and ceramic, all have the requisite hardness and stiffness for hard drive applications. However, each of these materials has its own particular problems.
Glass provides a hardness which is superior to aluminum with a small increase in stiffness. However, most glasses have alkaline metal ions present in their composition which may cause a corrosive effect known as a salt bloom. This chemical phenomena may additionally contribute to disk malfunction. Even after sputtering a magnetic layer, and wear layer, the glass is not completely sealed and corrosion problems may occur.
Glass/ceramics provide superior hardness and stiffness. However, glass ceramics cannot generally be super finished. Specifically, glass ceramics are difficult to polish while preventing other physical phenomenons during the polishing cycle. Because of hardness of glass/ceramics, finishing cycles are very long and the disks begin to adopt certain characteristics which are undesirable such as edge roll off.
Ceramic materials also provide superior stiffness and hardness when compared to aluminum substrates. However, due to the crystalline nature of ceramics, the material inherently has defects such as pits and holes. Further, due to the absolute hardness of ceramics, the material is difficult to super finish. One alternative to creating a hard disk from a ceramic composition is to fabricate the ceramic through a hot isostatic press processing. However, even with this extreme, the ceramic still retains porosity inherent in all ceramics but with substantially less defects.
However, nonmetallic composition such as glass, glass/ceramic and ceramic by themselves lack the properties necessary for use in memory storage applications such as computer disk drives. In order to improve the memory storage properties of all these nonmetallic materials, the surface coating/passivation must be undertaken. Surface coating/passivation can be achieved by plating a layer of nickel phosphorus onto the nonmetallic substrate. However, nickel phosphorous plating nonmetallic substrates generally fails due to poor adhesion. Plated materials can adhere to a substrate either chemically or mechanically. Plated materials do not tend to bond well to nonmetallic substrates. Thus, mechanical adhesion is a natural alternative. Unfortunately, nonmetallics such as glass, glass/ceramic and ceramic tend to be smooth and no mechanical bonding can be obtained.
As a result, there is a need for processes and resulting articles which resist defects, provide a smooth substrate surface, (to atomic smoothness), are relatively thin, have low mass and have high stiffness and hardness.